<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>天气案例_监视属性</title>
  <script src="../js/vue.js"></script>
</head>

<body>
  <div id="root">
    <h2>今天天气很{{info}}</h2>
    <button @click="isHot = !isHot">切换天气</button>
  </div>

  <script>
    Vue.config.productionTip = false

    const vm = new Vue({
      el: '#root',
      data: {
        isHot: true
      },
      computed: {
        info() {
          return this.isHot ? '炎热' : '凉爽'
        }
      },
      // watch: {
      //   isHot: {
      //     // 初始化时让handler调用一下
      //     immediate: true,
      //     // handler什么时候调用？当isHot发生改变时
      //     handler(newValue, oldValue) {
      //       console.log("newValue:",newValue,",oldValue:", oldValue)
      //     }
      //   }
      // }
    })

    vm.$watch('isHot', {
      immediate: true,
      handler: function (newValue, oldValue) {
        console.log('newValue:', newValue, ',oldValue:', oldValue)
      }
    })
  </script>
</body>

</html>